Adjusting playback speed is supposed to be a feature in the beta for MX Player [https://sites.google.com/site/mxvpen/translation/test-build] and I know the current version supports volume boost. It's my player of choice because I'm yet to find a file it won't play (though you'll need to install manually install this codec [http://www.phonearena.com/news/How-to-restore-full-audio-codec-support-AC3-DTS-in-MX-Player-Androids-best-video-playback-app_id64435] for licencing reasons), it supports video streams and remembers your playback position.